[PATCH v2] examples/packet_ordering: fix segfault in disable_reorder mode

[Qian Hao <qi_an_hao@126.com>]

The packet_ordering example works in two modes (opt via --disable-reorder):
  - When reorder is enabled: rx_thread - N*worker_thread - send_thread
  - When reorder is disabled: rx_thread - N*worker_thread - tx_thread
N parallel worker_thread(s) generate out-of-order packets.

When reorder is enabled, send_thread uses seq number generated in rx_thread
(L459) to enforce packet ordering. Otherwise rx_thread just sends any packet
it receives.

rx_thread writes sequence number into a dynamic field, which is only registered
by calling rte_reorder_create() (Line 741) when reorder is enabled. However,
rx_thread marks sequence number onto each packet no matter whether reorder is
enabled, overwriting the leading bytes in packet mbufs when reorder is disabled,
resulting in segfaults when PMD tries to DMA packets.

`if (!disable_reorder_flag) {...}` is added in rx_thread to fix the bug. The
test is inlined by the compiler to prevent any performance loss.

Signed-off-by: Qian Hao <qi_an_hao@126.com>
---
 examples/packet_ordering/main.c | 32 +++++++++++++++++++++++++-------
 1 file changed, 25 insertions(+), 7 deletions(-)

diff --git a/examples/packet_ordering/main.c b/examples/packet_ordering/main.c
index d2fd6f77e4..f839db9102 100644
--- a/examples/packet_ordering/main.c
+++ b/examples/packet_ordering/main.c
@@ -5,6 +5,7 @@
 #include <stdlib.h>
 #include <signal.h>
 #include <getopt.h>
+#include <stdbool.h>
 
 #include <rte_eal.h>
 #include <rte_common.h>
@@ -427,8 +428,8 @@ int_handler(int sig_num)
  * The mbufs are then passed to the worker threads via the rx_to_workers
  * ring.
  */
-static int
-rx_thread(struct rte_ring *ring_out)
+static __rte_always_inline int
+rx_thread(struct rte_ring *ring_out, bool disable_reorder_flag)
 {
 	uint32_t seqn = 0;
 	uint16_t i, ret = 0;
@@ -454,9 +455,11 @@ rx_thread(struct rte_ring *ring_out)
 				}
 				app_stats.rx.rx_pkts += nb_rx_pkts;
 
-				/* mark sequence number */
-				for (i = 0; i < nb_rx_pkts; )
-					*rte_reorder_seqn(pkts[i++]) = seqn++;
+				/* mark sequence number if reorder is enabled */
+				if (!disable_reorder_flag) {
+					for (i = 0; i < nb_rx_pkts;)
+						*rte_reorder_seqn(pkts[i++]) = seqn++;
+				}
 
 				/* enqueue to rx_to_workers ring */
 				ret = rte_ring_enqueue_burst(ring_out,
@@ -473,6 +476,18 @@ rx_thread(struct rte_ring *ring_out)
 	return 0;
 }
 
+static __rte_noinline int
+rx_thread_reorder(struct rte_ring *ring_out)
+{
+	return rx_thread(ring_out, false);
+}
+
+static __rte_noinline int
+rx_thread_reorder_disabled(struct rte_ring *ring_out)
+{
+	return rx_thread(ring_out, true);
+}
+
 /**
  * This thread takes bursts of packets from the rx_to_workers ring and
  * Changes the input port value to output port value. And feds it to
@@ -772,8 +787,11 @@ main(int argc, char **argv)
 				(void *)&send_args, last_lcore_id);
 	}
 
-	/* Start rx_thread() on the main core */
-	rx_thread(rx_to_workers);
+	/* Start rx_thread_xxx() on the main core */
+	if (disable_reorder)
+		rx_thread_reorder_disabled(rx_to_workers);
+	else
+		rx_thread_reorder(rx_to_workers);
 
 	RTE_LCORE_FOREACH_WORKER(lcore_id) {
 		if (rte_eal_wait_lcore(lcore_id) < 0)
-- 
2.34.1